Emergency braking apparatus for vehicle

ABSTRACT

A vehicle emergency brake system has a second brake for braking a vehicle by increasing the frictional resistance with the road surface, a millimeter wave radar for detecting any obstacle in an advancing direction, a pedal speed sensor for detecting the step-in speed of a brake pedal for actuating a first brake, and a controller for actuating the second brake. If hard braking by the first brake is detected by the pedal speed sensor, the controller determines whether the vehicle is going to crash into an obstacle detected by the radar. If a determination is made that it will collide, the second brake is actuated. Thus, it is possible to reliably actuate the second brake in an emergency.

TECHNICAL FIELD

The present invention relates to a vehicle emergency brake system forurgently avoiding collision of the vehicle.

BACKGROUND ART

When a vehicle is traveling on a road surface having a low frictioncoefficient, such as a frozen road, a wet paved road, or a dry pavedroad where sand is disposed, the grip of the tires with respect to theroad surface falls, so that the wheels tend to slip. Thus, heretofore,with a brake system for braking the rotation of wheels mounted on thevehicle (first brake), even if hard braking is activated, the brakingdistance may increase excessively so that the vehicle may collideagainst an obstacle, irrespective of whether the vehicle is traveling ata high speed or a low speed.

On a road surface having such a low friction coefficient, since thedegrees of slipping tend to be uneven for individual wheels, travel ofthe vehicle tends to be unstable, so that the vehicle may collideagainst an obstacle in an oblique direction. As means for allowingstable travel of a vehicle, such systems as an ABS (Antilock BrakeSystem), which detects the degree of slip for every wheel and controlsthe braking force of each wheel, and VSC (Vehicle Stability Control) forcontrolling the engine output and the braking force of the wheels bydetecting the steering tendency of the vehicle with a yaw rate sensorand a lateral acceleration sensor are used practically. But in order forthese systems to operate effectively, it is a prerequisite that the gripof the tires remain to a certain extent.

In order to avoid collision of a vehicle on a road surface having a lowfriction coefficient as mentioned above, apart from a conventional brakesystem, it is proposed to mount a second brake for braking the vehiclein a short distance by increasing the frictional resistance with theroad surface. As the second brake, there are ones which sprayslip-preventive materials such as sand and ice particles between thetires and the road surface (See for example patent documents 1 through3.), ones in which a liquid adhesive is applied to the tire surfaces tostick slip preventive materials to the tires (See for example patentdocument 4.), ones in which thawing of the frozen road is prevented byblowing cold air on the tires (See for example patent document 5.), onesin which a braking plate or a toothed braking wheel is pressed againstthe road surface (See for example patent documents 6 through 8.), andones in which the pressing force of the vehicle against the road surfaceis increased by inflating a gas bag outwardly of the vehicle (See forexample patent document 9.), etc. (patent document 1; unexamined JPpatent publication 4-38204, patent document 2; unexamined JP patentpublication 7-309101, patent document 3; unexamined JP patentpublication 8-25905, patent document 4; unexamined JP patent publication63-2706, patent document 5; unexamined JP patent publication 50-100703,patent document 6; unexamined JP patent publication 49-2228, patentdocument 7; unexamined JP patent publication 54-122528, patent document8; unexamined JP patent publication 8-40222, patent document 9unexamined JP patent publication 6-286586.)

DISCLOSURE OF THE INVENTION

Once the above-described second brake is actuated, it takes a long timeuntil it returns to normal, or it can never return to normal. Thus, itis desired to avoid unnecessary actuation and to actuate it only in anemergency where its actuation is indeed necessary. Therefore, an objectof the present invention is to provide an vehicle emergency brake systemwhich can accurately actuate the second brake.

In order to solve the above object, the vehicle emergency brake systemcomprises a first brake for braking the rotation of a wheel, a secondbrake for braking the vehicle by increasing frictional resistance with aroad surface, an obstacle detector means for detecting an obstacleexisting in an advancing direction, and a controllercontroller fordetermining whether or not the vehicle is going to crash into anobstacle detected by said obstacle detector means by a vehicle speed anddeceleration detector, wherein when it is determined that the vehicle isgoing to crash by said controllercontroller, said second brake isactuated.

As the obstacle detector means, it is possible to employ a method inwhich reflective waves off an obstacle of a laser, visible light,infrared beams, millimeter waves, radio waves, electromagnetic wavessuch as magnetism, or elastic waves such as ultrasonic waves, orsomething generated by the obstacle itself are detected by a sensor, aradar, a TV camera, etc., a method in which emission waves of suchelectromagnetic waves or elastic waves are beacons, a method in whichincoming waves are stereo-viewed or image-processed, or a method inwhich the GPS (Global Positioning System) or VICS (Vehicle InformationCommunication System) is used.

As the controller, it is possible to use a method in which calculationis made as to whether or not the vehicle is going to crash into anobstacle detected by the obstacle detector means from the distancebetween the obstacle and the vehicle and the vehicle speed andacceleration or deceleration.

A hard braking detector for detecting the actuation of hard braking bysaid first brake or actuation requirements for hard braking by a drivermay be provided so that if said actuation of hard braking or saidactuation requirements are detected, determination is made on whether ornot the vehicle is going to crash by said controller. Thus, it ispossible to reliably actuate the second brake in an emergency.

The vehicle emergency brake system may further comprise a hard brakingbooster for automatically boosting hard braking carried out by a driverthrough said first brake so that if it is determined that the vehicle iscrashing into an obstacle by said controller, said hard braking boosteris actuated, and if it is determined that the vehicle is still going tocrash into the obstacle, said second brake is actuated. Using the hardbraking booster, it is possible to reduce situations in which actuationof the second brake is necessary.

In an arrangement wherein said second brake may comprise a plurality ofdifferent types, wherein a road surface condition detector for detectingthe condition of a road surface is provided, and wherein according tothe road surface condition detected by the road surface conditiondetector, said second brake is selected from among the plurality ofdifferent types, it is possible to actuate a more effective type ofsecond brake according to the road surface condition.

That is, for example, a second brake of the type that sprays sandbetween a tire and a road surface is effective for a frozen road, but ona dry paved road where sand is disposed, it rather promotes slip ofwheels. Thus, by mounting a plurality of different types of brake means,and selectively using them, the second brake can be effectively actuatedaccording to various road surface conditions.

As the road surface condition detector, as with the ones described in JPpatent publications 7-112659 and 2002-120709, it is possible to employ amethod in which the road surface condition is indirectly inferred fromthe relation between the total sum of the slip values of the individualwheels and the vehicle acceleration, or from the frequency response oftransmission characteristics from road surface disturbance to wheelspeeds, or a method in which the road surface condition is directlyobserved with e.g. a TV camera.

In an arrangement in which after the second brake have been actuated, ifthere is no actuation of hard braking by said first brake, anddetermination is made that crashing of the vehicle into the obstaclewill be avoided by said controller, or if determination is made that thevehicle is at a stop, actuation of said second brake is stopped, it ispossible to save redundant use of slip preventive materials such as sandand ice particles or cold air blown against a tire during actuation ofthe second brake.

By producing an alarm sound when said second brake is actuated, thedriver and passengers can prepare themselves for e.g. collision duringactuation of the second brake. The alarm sound should be stopped whendetermination is made that collision of the vehicle has been avoided orwhen the actuation of the second brake has stopped.

Since the vehicle emergency brake system comprises a first brake forbraking the rotation of a wheel, a second brake for braking the vehicleby increasing frictional resistance with a road surface, an obstacledetector means for detecting an obstacle in an advancing direction, anda controller for determining whether or not the vehicle is going tocrash into an obstacle detected by said obstacle detector means by avehicle speed and deceleration detector, wherein when it is determinedthat the vehicle is going to crash by said controller, said second brakeis actuated, it is possible to reliably actuate the second brake in anemergency and avoid unnecessary actuation of the second brake, whichtakes time to return to normal.

A hard braking detector for detecting the actuation of hard braking bysaid first brake or actuation requirements for hard braking by a drivermay be provided so that if said actuation of hard braking or saidactuation requirements are detected, determination is made on whether ornot the vehicle is going to crash by said controller. Thus, it ispossible to reliably actuate the second brake in an emergency.

The vehicle emergency brake system may further comprise a hard brakingbooster for automatically boosting hard braking carried out by a driverthrough said first brake so that if it is determined that the vehicle iscrashing into an obstacle by said controller, said hard braking boosteris actuated, and if it is determined that the vehicle is still going tocrash into the obstacle, said second brake is actuated. Using the hardbraking booster, it is possible to reduce situations in which actuationof the second brake is necessary.

In an arrangement wherein said second brake may comprise a plurality ofdifferent types of brake means, wherein a road surface conditiondetector for detecting the condition of a road surface is provided, andwherein according to the road surface condition detected by the roadsurface condition detector, said second brake is selected from among theplurality of different types of brake means, it is possible to actuate amore effective type of second brake according to the road surfacecondition.

In an arrangement in which after the second brake have been actuated, ifhard braking by said first brake is not actuated, and determination bythe controller is made that crashing of the vehicle into the obstaclewill be avoided, or if determination is made that the vehicle is at astop, actuation of said second brake is stopped, it is possible to saveredundant use of slip preventive materials such as sand and iceparticles or cold air blown against a tire during actuation of thesecond brake.

By producing an alarm sound when said second brake is actuated, thedriver and passengers can prepare themselves for e.g. collision duringactuation of the second brake.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of a vehicle on which is mounted avehicle emergency brake system of a first embodiment, FIG. 2 is aschematic structural view showing a second brake of FIG. 1; FIG. 3 is aflowchart showing an algorithm for actuating the vehicle emergency brakesystem of FIG. 1, FIG. 4 is a schematic structural view of a vehicle onwhich is mounted a vehicle emergency brake system of a secondembodiment, FIG. 5 is a flowchart showing an algorithm for actuating thevehicle emergency brake system of FIG. 4, and FIG. 6 is a flowchartshowing an algorithm for actuating a vehicle emergency brake system of athird embodiment.

BEST MODE FOR EMBODYING THE INVENTION

Below, based on FIGS. 1 through 6, the embodiments of this invention aredescribed. FIGS. 1 through 3 shows the first embodiment. As shown inFIG. 1, this vehicle emergency brake system comprises a second brake 1for increasing the frictional resistance with the road surface byspraying a slip preventive material between the tires and the roadsurface, a radar 2 using millimeter waves for detecting any obstacle infront of the vehicle A, a pedal speed sensor 5 for detecting the step-inspeed of a brake pedal 4 for actuating a first brake (not shown) forbraking the rotation of the respective wheels 3, and a controller 6 fordetermining whether or not the vehicle A is going to crash into anobstacle detected by the radar 2 if hard braking by the first brake isactivated, and if determined that it will do, activating the secondbrake 1.

In the controller 6, the distance L to the obstacle, which is detectedby the radar 2, and the step-in speed S of the brake pedal 4, which isdetected by the pedal speed sensor 5, are input. A threshold ST of thestep-in speed 5, which is used as a reference for determination of hardbraking of the first brake, is preset. While not shown, the vehiclespeed V as detected by a vehicle speed sensor and the vehicleacceleration ? as detected by a vehicle acceleration sensor 18 are alsoinput in the controller 6.

As shown in FIG. 2, the second brake 1 accumulates gas in an accumulator8 with a pump 7, supplies the accumulated gas into a spray materialcontainer 11 in which is stored a slip preventive material through twosolenoid valves 9 and 10, opens the respective solenoid valves 9 and 10under the command from the controller 6 to spray the slip preventivematerial through a nozzle 12 provided in front of one of the wheels 3. Abypass path 13 provided between the solenoid valve 10 and the nozzle 12is provided for a test in which confirmation is made that the nozzle 12is not clogged and the second brake 1 operates normally, by blowing gasonly through the nozzle 12. While not shown, the solenoid valves 9 and10, the spray material container 11 and the nozzle 12 are provided foreach wheel 3. They may be provided only on the front wheel side, wherethe braking effect is large.

FIG. 3 is a flowchart showing the algorithm of the controller 6, whichactivates the vehicle emergency brake system. First, the controller 6compares the step-in speed 5, which is input from the pedal speed sensor5 at short intervals, with the preset threshold ST (Step 1), and if thestep-in speed S exceeds the threshold ST, it further checks if there isany obstacle on the radar 2 (Step 2), and if there is an obstacle, itcalculates the braking distance LB by the first brake from the vehiclespeed V and the vehicle acceleration (deceleration) a, which are inputfrom the vehicle speed sensor and the vehicle acceleration sensor 18,respectively, by the following formula (Step 3).LB=V2/(2?)  (1)

In Formula (1), the braking distance LB is calculated with thedeceleration by hard braking as a constant deceleration ?. The brakingcharacteristics by the first brake may be grasped beforehand so as tocorrect the braking distance LB, which is calculated by Formula (1),based on the braking characteristics.

Next, the calculated braking distance LB is compared with the distance Lto the obstacle detected by the radar 2 (Step 4), and if the brakingdistance LB exceeds the distance L to the obstacle, it determines thatthe vehicle is going to crash into the obstacle. Thus, it opens thesolenoid valves 9 and 10 to actuate the second brake 1 (Step 5).

In this embodiment, actuation of hard braking by the first brake is aprerequisite for actuating the second brake. But if actuationrequirements of hard braking by the driver are a prerequisite, there isa case in which no deceleration has started yet, and thus the estimationof braking distance LB is impossible. In such a case, if for example theoutput of a sensor for detecting actuation requirements for hard brakingexceeds a predetermined threshold, it preferably unconditionallydetermines that the vehicle is going to crash into the obstacle andactivates only the second brake 1. In this determination, the distance Lto the obstacle L and/or the vehicle speed V may be additionally takeninto consideration.

FIGS. 4 and 5 show the second embodiment. As shown in FIG. 4, thisvehicle emergency brake system is provided, besides the elements of thefirst embodiment, with a second brake 16 for pressing a braking plate 15against the road surface with a cylinder 14, and a TV camera 17 forobserving the road surface condition in front of the vehicle A.According to the road surface condition observed by the TV camera 17,the second brake 1 for spraying the slip preventive material and thesecond brake 16 for pressing the braking plate 15 against the roadsurface are selectively actuated by the controller 6.

The controller 6 determines from the road surface images picked up bythe TV camera 17 whether the road surface is frozen, wet or dry. Asdescribed above, the road surface condition may be indirectly inferredfrom the relation between the sum of the slip values of the respectivewheels and the vehicle acceleration, or frequency response oftransmission characteristics from road surface disturbance to the wheelspeeds.

FIG. 5 is a flowchart showing the algorithm of the controller 6, whichactuates the above vehicle emergency brake system. As with the one ofthe first embodiment, first, the controller 6 compares the step-in speed5, which is input from the pedal speed sensor 5 at short intervals, withthe threshold ST (Step 1), and if the step-in speed S exceeds thethreshold ST, it further checks if there is any obstacle on the radar 2(Step 2), and if there is an obstacle, it calculates the brakingdistance LB by the first brake from the vehicle speed V and the vehicleacceleration (deceleration) a by Formula (1). The calculated brakingdistance LB is compared with the distance L to the obstacle (Step 4).

If the braking distance LB exceeds the distance L to the obstacle, itdetermines if the road surface shot by the TV camera 17 is dry orotherwise (Step 5), and if it determines that the road surface is dry,the second brake 16 for pressing the braking plate 15 is actuated (Step6). Otherwise, the second brake 1 for spraying the slip preventivematerial is actuated (Step 7).

While not shown, in the vehicle emergency brake system of the thirdembodiment, in the controller 6 of the first embodiment, which is shownin FIG. 1, a brake assist system as a hard braking boosting means forautomatically boosting hard braking carried out by the driver throughthe first brake is mounted, and if the braking distance LB calculated byFormula (1) exceeds the distance L to the obstacle detected by the radar2, the brake assist system is actuated first, and if it still determinesthat the vehicle A is going to crash into the obstacle, the second brake1 is actuated.

FIG. 6 is a flowchart showing the algorithm of the controller 6 foractuating the vehicle emergency brake system of the third embodiment. Inthis flowchart, Step 1 in the first embodiment of FIG. 3 is omitted, andStep 41 for actuating the brake assist system, Step 42 for calculatingthe braking distance LB1 by the brake assist system, and Step 43 forcomparing the braking distance LB1 with the distance L to the obstacledetected by the radar 2 are provided in the YES path between Step 4 andStep 5 to actuate the second brake 1 if the braking distance LBL exceedsthe distance L to the obstacle.

If the hard braking booster such as the brake assist system is provided,steps for actuating the hard braking booster may be provided between theYES path between Step 1 and Step 2 in the flowchart of the firstembodiment, shown in FIG. 3 so as to make determination on vehiclecollision by calculating the braking distance LB by boosted hard brakingof the first brake and comparing it with the distance L to the obstacle.

In the above embodiments, as the obstacle detector means, a millimeterwave radar was used, and as the hard braking detector, a pedal speedsensor for the brake pedal was used. But these obstacle detector meansand hard braking detector are not limited to those of the embodiment,but various methods as described above can be employed. For the secondbrake, too, anything that can increase the frictional resistance withthe road surface may be used. That is, the above-described various meanscan be employed.

1. An emergency brake system for a vehicle comprising: a first brake forbraking the rotation of a wheel; a second brake for braking the vehicleby increasing frictional resistance with a road surface; an obstacledetector for detecting an obstacle existing in an advancing direction ofthe vehicle; a vehicle speed and deceleration detector for detecting thespeed and deceleration of the vehicle; a hard braking detector fordetecting the actuation of hard braking by said first brake or actuationrequirements for hard braking by a driver; and a controller fordetermining whether or not the vehicle is going to crash into theobstacle detected by said obstacle detector based on the speed anddeceleration detected by said vehicle speed and deceleration detector,after the actuation of hard braking or the actuation requirements havebeen detected by said hard braking detector; wherein said second brakeis actuated if said controller determines that the vehicle is going tocrash into the obstacle detected by said obstacle detector.
 2. Anemergency brake system for a vehicle as claimed in claim 1 furthercomprising a hard braking booster for automatically boosting hardbraking carried out by a driver through said first brake, wherein if itis determined that the vehicle is going to crash into an obstacle bysaid controller, said hard braking booster is actuated, and if it isdetermined that the vehicle is still going to crash into the obstacleafter actuation of the hard braking booster, said second brake isactuated.
 3. An emergency brake system for a vehicle as claimed in claim1 wherein said second brake comprises a plurality of different types ofbrakes, wherein a road surface condition detector for detecting thecondition of a road surface is provided, and wherein according to theroad surface condition detected by the road surface condition detector,said second brake is selected from among the plurality of differenttypes of brakes.
 4. An emergency brake system for a vehicle as claimedin claim 1 wherein after the second brake have been actuated, if hardbraking by said first brake is not actuated, and determination by saidcontroller is made that crashing of the vehicle into the obstacle willbe avoided or if determination is made that the vehicle is at a stop,actuation of the second brake is stopped.
 5. An emergency brake systemfor a vehicle as claimed in claim 1 wherein an alarm sound is producedwhen said second brake is actuated.